1. Field of the Invention
Embodiments of the present invention relate to the field of integrated circuits. More particularly, embodiments of the present invention relate generally to cooling systems for transferring thermal energy away from integrated circuits.
2. Related Art
The trend in decreasing the size of semiconductor components leads to smaller electronic devices that are computationally more powerful than their older counterparts. For example, mobile devices, such as cell phones and personal digital assistants, are packed with multiple functionalities that in the past were isolated to single devices. Cells phones that previously were limited to transmitting and receiving mobile phone calls, and possibly an address book, now function as phones, calendars, address books, cameras, etc. Moreover, these multiple functionalities are increasing from year to year. In addition, more powerful devices, such as laptop computers, also are enjoying an increase in computing power and reduced size.
To increase functionality in the same or smaller space for devices, various techniques can be employed to increase density in integrated circuits of the electronic devices. For instance, the silicon wafer upon which an integrated circuit chip or die is formed can be thinned. In some instances, the silicon wafer can be thinned by as much as 90 percent of its original thickness. In this way, electronic devices incorporating the thinner silicon wafer can also be made to be thinner. In addition, stacking multiple dies in a single package can increase the density of semiconductor components in an electronic device. As a result, if the dies in a stacked die configuration have been thinned, more dies can be incorporated within the same or smaller amount of space as compared to previous generations of an electronic device.
Thermal management of integrated circuits is of a primary concern especially in light of the continual decrease in size of electrical components and the devices that house those components. Typical systems and methods for cooling integrated circuits include active cooling techniques, such as fans for passing air over the integrated circuits to dissipate thermal energy. However, fans require battery power for operation which is problematic for battery operated devices. In addition, active cooling techniques employing fans require air flow through the electronic device for cooling, thereby requiring the electronic device to be of a sufficient size to accommodate air flow and cooling. This puts a minimum limit on the size of the electronic device. This minimum limit may be too large to accommodate the trend towards smaller devices.
In addition, heat sinks have been directly coupled to the die in order to dissipate its thermal energy. In one case, these heat sinks that are attached to the die can be cooled through direct transfer of thermal energy to air circulated by fans. In another case, the heat sinks circulate a cooling medium to a remote heat exchanger through which thermal energy is dissipated. In either case, the attached heat sinks negatively increase the size of the die. This in turn increases the size of the electronic device incorporating the die and the attached heat sink.
In addition, these traditional systems and methods provide limited cooling of stacked die configurations. For instance, an active cooling mechanism employing circulating air relies on maximizing the surface area on the die for the transfer of thermal energy. However, in a stacked die configuration, exposed surface area of the die is significantly reduced, thereby reducing the effectiveness of active cooling systems incorporating the circulation of air. For example, the middle die in a three die stacked die configuration has very limited surface area for dissipating heat. Also, attaching a heat sink to the top of a die stacked configuration only effectively cools the uppermost die of the stacked die configuration, resulting in limited or no cooling of the lower die in the stacked die configuration.
As a result, traditional cooling systems and cooling methods for integrated circuits provide limited cooling as the density of components increases on dies, either through the shrinkage in size of the electrical components, or through a combination of component shrinkage and the placement of dies in a stacked die configuration.